This invention relates to a dispensing system, and more particularly, it related to a pressure modulated dispensing system suitable for use with molten metals such as molten aluminum, for example, to avoid splashing and the attendant oxidation of the metal.
As noted in my U.S. Pat. No. 6,049,067, incorporated herein by reference, aluminum is frequently delivered to customers in molten form. The benefits are substantial energy savings and product availability in a ready-for-use (molten) condition. Trailer mounted transport crucibles are used for this purpose. Since the heat loss from these crucibles is high, transport time is limited to a few hours, and considerable superheat must be added to the metal to ensure delivery at minimum acceptable temperature. It is common practice to heat molten aluminum to temperatures above 1700xc2x0 F. for the purpose of adding sufficient superheat. Direct impingement gas fired burners are used for this purpose.
Further, as noted, high temperature is undesirable because it increases metal oxidation rate which generates skim. Melt loss can exceed 10%. Further, metal quality rapidly deteriorates since hydrogen solubility in aluminum is an exponential function of temperature, and oxides are formed. Refractory life is reduced by high temperature, and wall accretions build up and limit crucible metal capacity. The hazards associated with handling molten aluminum increase significantly with elevated temperature.
Another problem with molten metal such as molten aluminum involves transferring molten metal to and from the container or crucible because this requires the control of metal flow rate. The flow rate control is needed for operating, quality and safety considerations. The conventional means for controlling metal flow rate, for example, from a ladle by gravity includes varying the area available for metal flow. That is, when an orifice is positioned in the bottom of a ladle the size of the area of the orifice is change to change the molten metal flow rate. Conventional means used to change the orifice area include a tapered rod or sometimes a slide gate. However, these provide no means for controlling molten metal flow rate other than by varying the orifice area. Thus, when the ladle is is full of molten metal, there is great force on the orifice, which when opened result metal splashing and a hazardous situation. Further, there is an increase in oxides and reduced metal quality, particularly with molten aluminum, which readily oxides.
Thus, there is a great need for a molten metal dispensing system which provides greater flow control and minimizes splashing.
It is an object of the invention to provide an improved molten metal dispensing means.
It is another object of the invention to provide a pressure modulated molten metal transfer system.
It is still another object of the invention to provide an improved system employing pressure modulation for transferring molten metal such as molten aluminum from a reservoir such as a ladle.
These and other objects will become apparent from the specification, drawings and claims appended hereto.
In accordance with these objects, there is disclosed a method of dispensing or pouring molten metal, e.g., aluminum, from a container or vessel, the flow rate controlled to minimize splashing of the molten aluminum exiting the container, the method comprising the steps of providing a container for containing molten metal, the container having an outlet for dispensing molten metal therefrom and providing a body of molten aluminum in the container, the body having a top surface. A pressure lower than atmospheric pressure is maintained on the surface of the body in the container vessel for purposes of controlling the flow of molten metal through said outlet. Molten metal is dispensed through the outlet by increasing the pressure maintained in the container towards atmospheric pressure.
The invention includes an improved container for containing molten metal for dispensing molten metal therefrom at a controlled flow rate to minimize splashing of the molten aluminum exiting the container. The invention comprises a container for containing a body of molten metal, the body having a surface, the container having: (i) an outlet for dispensing molten metal therefrom, and (ii) a lid for closing the container. Means is provided for reducing pressure on the surface of said body below atmospheric pressure to provide a reduced pressure. Means is provided for increasing the reduced pressure towards atmospheric for purposes of controlling the flow rate of molten metal through the outlet of the container.